SERVER-27745: Implement LogicalClock

1 files changed, 118 insertions, 0 deletions

diff --git a/src/mongo/db/logical_clock.cpp b/src/mongo/db/logical_clock.cpp
new file mode 100644
index 00000000000..c712941dee5
--- /dev/null
+++ b/src/mongo/db/logical_clock.cpp
@@ -0,0 +1,118 @@
+/**
+ *    Copyright (C) 2017 MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/db/logical_clock.h"
+
+#include "mongo/base/status.h"
+#include "mongo/db/operation_context.h"
+#include "mongo/db/service_context.h"
+#include "mongo/db/time_proof_service.h"
+#include "mongo/platform/basic.h"
+
+namespace mongo {
+
+namespace {
+const auto getLogicalClock = ServiceContext::declareDecoration<std::unique_ptr<LogicalClock>>();
+}
+
+LogicalClock* LogicalClock::get(ServiceContext* service) {
+    return getLogicalClock(service).get();
+}
+
+LogicalClock* LogicalClock::get(OperationContext* ctx) {
+    return get(ctx->getClient()->getServiceContext());
+}
+
+void LogicalClock::set(ServiceContext* service, std::unique_ptr<LogicalClock> clockArg) {
+    auto& clock = getLogicalClock(service);
+    clock = std::move(clockArg);
+}
+
+LogicalClock::LogicalClock(ServiceContext* serviceContext,
+                           std::unique_ptr<TimeProofService> tps,
+                           bool validateProof)
+    : _serviceContext(serviceContext),
+      _timeProofService(std::move(tps)),
+      _validateProof(validateProof) {}
+
+SignedLogicalTime LogicalClock::getClusterTime() {
+    stdx::lock_guard<stdx::mutex> lock(_mutex);
+    return _clusterTime;
+}
+
+SignedLogicalTime LogicalClock::_makeSignedLogicalTime(LogicalTime logicalTime) {
+    return SignedLogicalTime(logicalTime, _timeProofService->getProof(logicalTime));
+}
+
+Status LogicalClock::advanceClusterTime(const SignedLogicalTime& newTime) {
+    if (_validateProof) {
+        invariant(_timeProofService);
+        auto res = _timeProofService->checkProof(newTime.getTime(), newTime.getProof());
+        if (res != Status::OK()) {
+            return res;
+        }
+    }
+
+    stdx::lock_guard<stdx::mutex> lock(_mutex);
+    // TODO: rate check per SERVER-27721
+    if (newTime.getTime() > _clusterTime.getTime()) {
+        _clusterTime = newTime;
+    }
+
+    return Status::OK();
+}
+
+LogicalTime LogicalClock::reserveTicks(uint64_t ticks) {
+
+    invariant(ticks > 0);
+
+    stdx::lock_guard<stdx::mutex> lock(_mutex);
+
+    const unsigned wallClockSecs =
+        durationCount<Seconds>(_serviceContext->getFastClockSource()->now().toDurationSinceEpoch());
+    unsigned currentSecs = _clusterTime.getTime().asTimestamp().getSecs();
+    LogicalTime clusterTimestamp = _clusterTime.getTime();
+
+    if (MONGO_unlikely(currentSecs < wallClockSecs)) {
+        clusterTimestamp = LogicalTime(Timestamp(wallClockSecs, 1));
+    } else {
+        clusterTimestamp.addTicks(1);
+    }
+    auto currentTime = clusterTimestamp;
+    clusterTimestamp.addTicks(ticks - 1);
+
+    _clusterTime = _makeSignedLogicalTime(clusterTimestamp);
+    return currentTime;
+}
+
+void LogicalClock::initClusterTimeFromTrustedSource(LogicalTime newTime) {
+    invariant(_clusterTime.getTime() == LogicalTime::kUninitialized);
+    _clusterTime = _makeSignedLogicalTime(newTime);
+}
+
+}  // namespace mongo